**5. Imaging evaluation of cerebral embolism**

Although all devices have a common goal of preventing the entry of particles into distal circulation, the perfect protection system does not exist [42]. Among proximal protection systems with balloons, arterial occlusion is the weakest point because patients might not tolerate it. Moreover, the contrast of vessels during the CAS is difficult because of flow stagnation, which makes positioning the stent difficult. Moreover, this system is more laborious and complex to use than filters. Additionally, proximal protection systems are very high profile and tend to lead to hemorrhaging complications at the puncture site. The device's advantages include its ability to initiate cerebral protection at an early stage and to avoid

**Figure 2.** Examples of cerebral protection devices: eccentric design (A) in the EPI® filter and concentric design (B) in

The distal embolic protection devices with a balloon have the disadvantage of preventing antegrade flow, which renders some patients intolerant of this type of device. The balloon may also cause vascular lesions (example: pseudoaneurysm), and the affixture of the balloon may be lost during the CAS. Moreover, images cannot be easily obtained while the balloon is in use and, technically, the balloon is not very maneuverable. An advantage of distal protection

Among the disadvantages of distal embolic protection devices with filters is that they may not capture all particles and their delivery and recovery systems may cause embolisms. Some filters may attach to the stent because of bad handling. The advantages of filters include the preservation of antegrade flow to the brain during all stages of the CAS and the ability to obtain graphic images easily. Some systems allow the operator to select which guide wire to use to cross the lesion, which allows the filter to remain in contact with the arterial wall and the guide

embolization during the initial passage of the wire through the stenosis [13,42].

the Emboshield® system

154 Carotid Artery Disease - From Bench to Bedside and Beyond

devices is their ease of use compared with proximal occlusion balloons [13].

wire to be moved during the CAS without mobilizing the filter [13].

We consider MRI an excellent method for evaluating cerebral ischemia in its various presen‐ tations. An MRI study of various acute neurological presentations of an ischemic nature includes several forms of ischemia presentation on the images [64].

Diffusion (DWI) is the best MRI technique to differentiate ischemia from chronic infarction. While the latter shows an increase in diffusion, the former classically restricts diffusion [65]. The identification of acute lesions in patients with multiple chronic lesions makes DWI a tool of unquestionable value in current imaging practice.

**6. Methods**

cranial arteries.

quadrature").

("nex"): 1

of coronary angina and hemodynamic instability.

**•** Coefficient of apparent diffusion: map of "ADC"

ms, bandwidth 15.63 and number of acquisitions: 2

4750 ms, bandwidth 31.25 and number of acquisitions: 2

Our sample consisted of 40 patients presenting carotid stenosis of atherosclerotic origin. The patients were referred for MRI exams with diffusion techniques before and after CAS. All of the patients in this prospective study signed an informed consent form. The inclusion criteria were as follows: patients with serious carotid stenosis (shown by Doppler, ATC, or digital subtraction angiography [DSA]) who were referred for endovascular treatment for carotid atheromatous disease according to the local institutional guidelines, who agreed to participate in the research protocol, and who had MRI studies conducted with diffusion techniques at

Cerebral Protection in Carotid Angioplasty – Is There a Need? Advantages and Disadvantages of...

http://dx.doi.org/10.5772/57154

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Exclusion criteria were the following: intra-arterial thrombi observed in the angiography before CAS; patients with disabling complications from previous cerebral infarcts; contrain‐ dications for the MRI scan, such as a cardiac pacemaker or claustrophobia, patients with macroemboli in the DSA after CAS, clinical conditions compatible with ischemia after CAS, angiographic exam showing stenosis <60%, MRI exams with movement artifacts, and imaging studies with serious stenosis in the contralateral cervical carotid, vertebral arteries, or intra‐

Three patients out of 40 were excluded because they showed stenosis <60%, and one patient was excluded for having exceeded the maximum time established for MRI after CAS because

The MRI studies were performed using commercially available single high-field equipment (1.5 T, LX Horizon®, General Electric Healthcare) with a skull coil ("birdcage transmit/receive

**•** Locator: 256x128 matrix, FOV 27 cm, 10 mm thickness, 5 mm spacing, number of acquisitions

**•** DWI: 128X128 matrix, FOV 22 cm, 5 mm thickness, 0 mm spacing, TE minimum 72.8 ms, TR 9000 ms, "b-value" 0 and 1000, diffusion direction: "all", number of acquisitions: 2

**•** T2W, axial, 288x224 matrix, FOV 22 cm, 6 mm thickness, 0.6 mm spacing, TE 102 ms, TR

**•** T1W, axial, 256x192 matrix, FOV 22 cm, 6 mm thickness, 0.6 mm spacing, TE 14 ms, TR 475

**•** Fluid-attenuated inversion recovery (FLAIR): axial, 256x192 matrix, FOV 22 cm, 6 mm thickness, 0.6 mm spacing, TE 96 ms, TR 10000 ms, TI 2.100 ms and number of acquisitions: 1

**•** T2W, coronal, 288x224 matrix, FOV 22 cm, 6 mm thickness, 0.6 mm spacing, TE 102 ms, TR

4750 ms, echo train length 23, bandwidth 31.25 and number of acquisitions: 2

The MRI scans before and after CAS followed the same sequencing protocol:

most 24 hours before and up to 72 hours after the CAS with a protection filter.

Water in tissues has a randomized translational movement ("Brownian motion") in its molecules caused by thermodynamic energy and the viscosity of the medium. This type of movement is related to CDA, and MRI uses DWI to evaluate it [66,67].

Diffusion imaging is sensitive to the microscopic movement of water protons. Water protons undergo a change during the transverse magnetization phase in the presence of a magnetic field gradient. Thus, areas with greater diffusion (faster movement) are subject to a high degree of signal attenuation compared with areas with lower diffusion (slow/restricted movement), which show lower signal attenuation. Animals subjected to occlusion of the middle cerebral artery (MCA) showed signs of ischemia in diffusion within 45 minutes. These findings are believed to reflect the restriction of water movement by the cellular membrane. MRI's greater sensitivity for detecting acute ischemia in diffusion is believed to be a result of the movement of water within the cell, which restricts the movement of water protons (cytotoxic edema), while the T2-weighted images show a signal change that results mainly from vasogenic edema. It is estimated that cytotoxic edema begins very soon after ischemic abuse, while the vasogenic edema begins to develop 6 hours after the ischemic incident.

Moseley et al. [65] argued that significant diffusion decrease (restriction or reduction) in ischemia reflects the deviation of an environment with extracellular water protons with a faster diffusion to a more restricted intracellular environment, in addition to the depletion of the sodium-potassium pump in the cellular membrane because of infarction. The cytotoxic edema is thus responsible for reducing diffusion during ischemia.

Nonetheless, the diffusion of ischemia areas can be reversed after early reperfusion and are potentially reversible if they occur after CAS. It has also been shown that ischemic lesions in diffusion might not leave changes that appear in later MRI scans after TIA frames.

The embolic complications identified in DWI occur more frequently than the apparent low rate of clinical complications would suggest. An MRI may quantify the ischemic foci, making it an important method for validating the advantages and complications of CAS.

To examine this issue more deeply, we conducted a prospective randomized study (patients chosen randomly from the outpatient neuroradiology service of INCOR) in a case-control setting [68]. We used angiographic exams and MRI studies that showed cerebral embolism represented by the diffusion sequence (DWI) before and after surgical endovascular treatment to quantify, locate, and measure new restriction foci in diffusion MRI and to correlate the new DWI restriction foci with demographic aspects (gender, age, side of the carotid treated, and symptoms), risk factors for cerebrovascular disease, aspects of the angioplasty technique used, and the presence of previous infarcts in MRI.
